Time Zones

The Earth takes 24 hours to rotate once on its axis. (This makes a day). It rotates 360° in a 24 hour period, so the Earth rotates at a rate of about 15° per hour. Therefore, the Earth has been divided into 24 time zones.

For centuries people figured the time of day by the sun’s position in the sky. Each day the sun rises on the eastern horizon, moves across the sky and sets in the west. Noon is the when the sun is at the highest point in its arc across the sky. (But it is NOT noon at the same time all over the world, because of Earth’s rotation).

The sun moves westward about 15° each hour, or about 1° every four minutes. (So, New York City is at 74°W and Philadelphia is at 75°W, so noon in New York City occurs about 4 minutes before it does in Philly.

Time Zones are a geophysical world globe division of 15o each, starting at Greenwich, England, created to help people know what time it is now in another part of the world (see page 76 in your text for a good Time Zone tool).These lines on a globe are called:Time Meridians.

International Date Line

0 degrees Longitude

0

-1 +1

-11

+10

The starting point for the standard time zones is the Prime Meridian, 0° (which passes through Greenwich, England)

If you move westward from Greenwich (back towards US) then you move your clock back to earlier time, while if you move eastward from Greenwich (further into Europe) you would set your clock to a later time.

Ex.) If its 10am in Greenwich (at 0°), then it is 11am in Rome (at 15°E).

Is Point C 2 hours ahead or behind A?So if its 7:00 at Point A, what time is it at Point B?

A

B

C

In theory each time zone should be exactly 15°wide, but time zones are adjusted to preventcities and certain areas from being split into 2 time zones. (That’s why you see the time zone lines look a little jagged).

When going completely around the world you will gain or lose time at each time zone until you have gained or lost an entire day.

• The International Date Line is the imaginary line (at 180°) at which the date changes.

– If you move west (to the left) across the IDL, you gain a day, if you move east(to the right) across the IDL it is one day earlier.

INTERNATIONAl

DATE

LINe

INTERNATIONAL

DATE

LINE

So its Friday here

Its Saturday here

If its Thursday here in Australia, and you sail across the IDL to Hawaii, what day is it there?

US Time ZonesWhat time zone does Montana fall under?

So if it 11am in VA, what time is it in NV?

Who will see the sun rise first – me here in Virginia or my friend out in California?

I want to call my brother in TX at 5:00pm tonight, what time is that my time here in VA?

Every day ½ the world is in day while the other ½ is in _____________.